Generally, one carrier is mainly taken into consideration in a wireless communication system although an uplink and a downlink are set to differ from each other in bandwidth. For instance, based on a single carrier, it may be able to provide a wireless communication system, in which the number of carrier configuring each of uplink and downlink is set to 1 and in which bandwidths of the uplink and downlink are symmetric to each other in general.
According to ITU (international telecommunication union), a technology candidate for IMT-Advanced is requested to support a bandwidth extended more than that of a conventional wireless communication system. Yet, frequency allocation of wider bandwidth is not globally available for many areas except some particular areas. As a technology for using fragmented small bands efficiently, there is an ongoing development of carrier aggregation (e.g., bandwidth aggregation, spectrum aggregation, etc.) to bring the same effect of using a band of logically wider bandwidth by physically bundling a plurality of bands together.
Carrier aggregation is introduced to support an increasing throughput, prevent a cost increase due to an introduction of a broadband RF device, and secure compatibility with a legacy system. Carrier aggregation is the technology for enabling data to be exchanged between a user equipment and a base station through a plurality of bundles of carriers by bandwidth unit defined in a legacy wireless communication (e.g., LTE system in case of LTE-A system, IEEE 802.16e system in case of IEEE 802.16m system). In this case, a carrier of a bandwidth unit defined in a legacy wireless communication system may be called a component carrier (hereinafter abbreviated CC). For instance, the carrier aggregation technology may include a scheme of supporting a system bandwidth up to maximum 100 MHz by making a bundle of maximum 5 CCs despite that one CC supports a bandwidth of 5 MHz, 10 MHz or 20 MHz.
If the carrier aggregation technology is adopted, a user equipment is able to transceive data with a base station through a plurality of uplink component carrier (hereinafter abbreviated UL CCs) and a plurality of downlink CCs (hereinafter abbreviated DL CCs). And, a physical random access channel (PRACH) resource capable of carrying a random access preamble may be set for each of the UL CCs.
The PRACH resource may be set in a time domain and frequency domain. Setting information on this PRACH resource may differ for each UL CC. Since UL CCs use different frequencies (or antenna positions), respectively, the UL CC may differ from each other in channel quality due to mobility of a user equipment or interference with a neighbor cell.